The laboratory numbers do not reflect the full extent of the flu, as most people do not get tested.

Prof Rawlinson said about two million people will be infected with the flu in a busy year, although only about a quarter or less are actually measured because most people do not get tested.

“I would predict a couple of million this year,” he said on Tuesday.

“It’s likely this will be the highest number since 2017 although I’d be very concerned that it may be higher because we haven’t seen so much in 2018.”

Experts expect there will be about 4000 deaths due to complications to do with the flu.

Immunisation Coalition chairman Professor Robert Booy said the actual number of deaths on average each season was about 3000 to 4000.

“I’m not saying we’re getting more deaths this year than any other year,” he said.

“We’ve got a very busy early season but it’s nothing like the peak that we had in 2017.”

Prof Booy said there has been a sustained and rising summer and autumn surge.

“The best explanation is that 2018 was so quiet that we have reduced community immunity, so there are more people who are vulnerable to catching infection and therefore transmitting infection,” he said.